With reference to FIG. 8, a prior art tri-eccentric valve structure is illustrated. Such kind of valve has been disclosed in some prior art, such U.S. Pat. No. 4,284,264, CN00229687, CN02209840, and CN200820221520.
In FIG. 1, the prior art disk valve has a valve body 1′ having a chamber 10′, a stem 2′ passing through the valve body 1′ to the chamber 10′; an annular seat 30′ installed in the chamber 10′; and an drain-proof ring 32′ which is an O ring. The drain-proof ring 32′ is asymmetric to an axis passing through a center of the ring. A valve disk 31′ is installed to the valve disk 31′. A radial hole radially passes through the valve disk 31′ for receiving the stem 2′ for controlling the valve disk 31′ to open or close.
The drain-proof ring is a tri-eccentric structure. That is, referring to FIG. 4, a longitudinal radial line of the valve disk is shifted from a longitudinal radial line of the valve body, this is so-called first shift (A′); an axial center of the valve disk is shifted from the center of the valve body, this is so-called second shift (B′); the valve disk 31′ is an asymmetric taper so as to form as a third shift (C′). Since in the prior art, the valve disk 31′ is an asymmetric taper (see FIG. 7) and thus the drain-proof ring 32′ received in an annular trench of the valve disk 31′ is also an asymmetric structure for tightly contracting the annular seat 30′ received in the inner annular wall of the valve body 1. As a result, every radial part of the drain-proof ring 32′ is critically defined to match the shape of the annular seat 30′. Thus, it is very difficult to manufacture this ring. Furthermore, a slight rotation of the drain-proof ring 32′ with respect to the annular seat 30′ will induce gaps between the valve body and the valve disk and thus fluid will drain out from one side of the valve to another side.
As illustrated in FIGS. 7 and 8, it is illustrated that in the prior tri-shifting valve, a lower side of the valve is horizontal and the upper side thereof is inclined. The slopes of sides between the upper and lower sides are between the slope of the horizontal line and the slope of the included line of the upper side. As a result, the edges of the drain-proof ring 32′ (see FIG. 7) are asymmetrical with respect to the middle axial line. This induces the difficulties in manufacturing process because it must be precise to form the desired shape. Furthermore, in installing the drain-proof ring, the positioning of the ring must be very accurately to fit the shape of the annular seat around the ring so that the drain-proof ring can completely seal the two sides of the valve. Moreover, the slight rotation of the ring will destroy the seal.
Therefore, there is an eager demand for a novel design which can improve the above mentioned defects.